The present invention relates generally to microelectromechanical (MEM) devices. The invention is thought to be advantageous when producing drop-on-demand liquid emission devices such as, for example, ink jet printers, and more particularly such devices which employ an electrostatic actuator for driving liquid from the device.
Drop-on-demand (DOD) liquid emission devices with electrostatic actuators are known for ink printing systems. U.S. Pat. Nos. 5,644,341 and 5,668,579, which issued to Fujii et al. on Jul. 1, 1997 and Sep. 16, 1997, respectively, disclose such devices having electrostatic actuators composed of a diaphragm and opposed electrode. The diaphragm is distorted by application of a first voltage to the electrode. Relaxation of the diaphragm expels an ink droplet from the device. Other devices that operate on the principle of electrostatic attraction are disclosed in U.S. Pat. Nos. 5,739,831, 6,127,198, and 6,318,841; and in U.S. Publication No. 2001/0023523.
U.S. Pat. No. 6,345,884, teaches a device having an electrostatically deformable membrane with an ink refill hole in the membrane. An electric field applied across the ink deflects the membrane and expels an ink drop.
IEEE Conference Proceeding xe2x80x9cMEMS 1998,xe2x80x9d held Jan. 25-29, 2002 in Heidelberg, Germany, entitled xe2x80x9cA Low Power, Small, Electrostatically-Driven Commercial Inkjet Headxe2x80x9d by S. Darmisuki, et al., discloses a head made by anodically bonding three substrates, two of glass and one of silicon, to form an ink ejector. Drops from an ink cavity are expelled through an orifice in the top glass plate when a membrane formed in the silicon substrate is first pulled down to contact a conductor on the lower glass plate and subsequently released. There is no electric field in the ink.
U.S. Pat. No. 6,357,865 by J. Kubby et al. teaches a surface micromachined drop ejector made with deposited polysilicon layers. Drops from an ink cavity are expelled through an orifice in an upper polysilicon layer when a lower polysilicon layer is first pulled down to contact a conductor and is subsequently released.
One such device is disclosed in co-pending U.S. patent application Ser. No. 10/122,566 entitled DROP-ON-DEMAND LIQUID EMISSION USING INTERCONNECTED DUAL ELECTRODES AS EJECTION DEVICE filed in the names of Christopher N. Delametter et al. on Apr. 15, 2002. That device includes a liquid chamber having a nozzle orifice. Separately addressable dual electrodes are positioned on opposite sides of a stationary central electrode such that the three electrodes are generally axially aligned with the nozzle orifice. The two addressable electrodes are structurally connected via a rigid, electrically insulating coupler. To eject a drop, an electrostatic voltage is applied to the addressable electrode nearest to the nozzle orifice, which pulls that electrode toward the central electrode and away from the orifice so as to draw liquid into the expanding chamber. Subsequently, the other addressable electrode is energized, pressurizing the liquid in the chamber behind the nozzle orifice and causing a drop to be ejected from the nozzle orifice.
The device described in the Delametter et al. patent application, and other multi-layer microelectromechanical electrostatic actuators for liquid emission devices, can be manufactured by chemical mechanical polishing in combination with a sacrificial layer to produce a planar surface with a non-sacrificial material that can move within a trench left when the sacrificial layer is removed to provide a separation from stationary parts.
According to a feature of the present invention, a multi-layer microelectromechanical electrostatic actuator for producing drop-on-demand liquid emission devices is made by forming an initial patterned layer of sacrificial material on a substrate. A first electrode layer is deposited and patterned on the initial layer at a position opposed to the substrate. Next, a subsequent patterned layer of sacrificial material is formed on the first electrode layer such that a region of the first electrode layer is exposed through the subsequent layer of sacrificial material. A second electrode layer is deposited and patterned on the subsequent layer of sacrificial material at a position opposed to the first electrode layer. Then, a third patterned layer of sacrificial material is formed on the second electrode layer, the third layer of sacrificial material having an opening there through to the exposed region of the first electrode layer. A structure is deposited and patterned on the third layer of sacrificial material to a depth to at least fill the opening through the third layer of sacrificial material. Next, the structure is planarized to expose a surface of the third layer of sacrificial material. A third electrode layer is deposited and patterned on the planarized structure and the exposed surface of the third layer of sacrificial material, whereby the first electrode layer and the third electrode layer are attached by the structure. Finally, the sacrificial material is removed from the initial layer, the subsequent layer, and the third layer, whereby the first electrode layer, the structure, and the third electrode layer are free to move together relative to the second electrode layer.